How to Block CSS and Image Requests in chromedp (Go)

Use Chrome DevTools Protocol’s Network domain before navigation. In chromedp, call network.SetBlockedURLs with URL patterns for stylesheets and image extensions, then navigate. This prevents matching requests from loading. If you must classify requests by browser resource type rather than filename, use the Fetch domain and explicitly fail paused requests.

Choose the blocking method

Start with Network blocking when extensions such as .css, .png and .webp are reliable indicators. Move to Fetch when URLs are opaque, resources are generated dynamically, or you need a decision for each request.

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Prerequisites and version checks

• A Go module using github.com/chromedp/chromedp and its generated github.com/chromedp/cdproto package.
• A Chrome or Chromium binary compatible with the CDP version used by your pinned cdproto module.
• A target context created by chromedp. Apply the blocking command to that target before calling chromedp.Navigate.

The generated API and enum names can change with module versions. Check the exact cdproto version in your go.mod and the browser version deployed by your application before copying a snippet into production.

Block CSS and common image extensions with Network.setBlockedURLs

Complete Go example

This example creates a browser context, installs URL rules, navigates, waits for the body, and captures a screenshot. The regular-expression-like backslashes shown in the patterns are part of the CDP URL-pattern syntax; verify escaping against your pinned generated package.

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package main

import (
    "context"
    "log"
    "time"

    "github.com/chromedp/cdproto/network"
    "github.com/chromedp/chromedp"
)

func main() {
    ctx, cancel := chromedp.NewContext(context.Background())
    defer cancel()

    ctx, cancel = context.WithTimeout(ctx, 45*time.Second)
    defer cancel()

    patterns := []*network.BlockPattern{
        {URLPattern: "*://*/*\.css*", Block: true},
        {URLPattern: "*://*/*\.png*", Block: true},
        {URLPattern: "*://*/*\.jpg*", Block: true},
        {URLPattern: "*://*/*\.jpeg*", Block: true},
        {URLPattern: "*://*/*\.webp*", Block: true},
        {URLPattern: "*://*/*\.gif*", Block: true},
    }

    err := chromedp.Run(ctx,
        chromedp.ActionFunc(func(ctx context.Context) error {
            return network.SetBlockedURLs().
                WithURLPatterns(patterns).
                Do(ctx)
        }),
        chromedp.Navigate("https://example.com"),
        chromedp.WaitVisible("body", chromedp.ByQuery),
        chromedp.CaptureScreenshot(nil, nil),
    )
    if err != nil {
        log.Fatal(err)
    }
}

Replace the final screenshot action with your own extraction or save action. The key ordering is the Network command first and navigation second. Installing rules after navigation can allow early CSS or image requests to complete before the filter exists.

Pattern details

• The patterns above target URLs containing the listed suffixes. A query string after the extension is still covered by the trailing wildcard.
• Add other extensions used by your site, such as .svg or .avif, only when you intentionally want those resources blocked.
• URL blocking is not MIME-type inspection. An image served from /asset?id=42 will not match an extension rule.
• Rules are ordered. A matching allow pattern (Block: false) can permit a URL even when another rule would block it, so review overlapping rules carefully.

Allow one exception

If a page needs one stylesheet but you want to block other CSS, add an allow pattern for that URL according to the generated API’s ordering semantics, then add the broader block pattern. Test the exact order with your module and browser; do not assume a different CDP release resolves overlaps identically.

Filter by resource type with Fetch

Fetch interception is appropriate when the URL does not reveal whether a request is CSS or an image. Enable request patterns that include the URL pattern and the browser resource type, listen for paused requests, and fail only the matches you want to suppress. Continue every other paused request.

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// Illustrative structure: confirm Fetch type and method names in your pinned cdproto.
patterns := []*fetch.RequestPattern{
    {URLPattern: "*", ResourceType: network.ResourceTypeStylesheet, RequestStage: fetch.RequestStageRequest},
    {URLPattern: "*", ResourceType: network.ResourceTypeImage, RequestStage: fetch.RequestStageRequest},
}

err := chromedp.Run(ctx, chromedp.ActionFunc(func(ctx context.Context) error {
    return fetch.Enable().WithPatterns(patterns).Do(ctx)
}))
if err != nil {
    return err
}

chromedp.ListenTarget(ctx, func(ev interface{}) {
    paused, ok := ev.(*fetch.EventRequestPaused)
    if !ok {
        return
    }

    // Decide from paused.ResourceType (or your own URL rules).
    if paused.ResourceType == network.ResourceTypeStylesheet ||
        paused.ResourceType == network.ResourceTypeImage {
        go func() {
            _ = chromedp.Run(ctx, fetch.FailRequest(paused.RequestID, network.ErrorReasonBlockedByClient))
        }()
        return
    }

    go func() {
        _ = chromedp.Run(ctx, fetch.ContinueRequest(paused.RequestID))
    }()
})

The exact generated names for ResourceType, request stages, events, and failure reasons vary by cdproto version. Treat this as the implementation shape: enable Fetch, handle every paused event, fail CSS and image requests, and continue all others. Register the listener early enough that requests cannot accumulate before a handler is attached.

Why an unhandled paused request is dangerous

Fetch patterns pause matching requests until the client responds. If your listener panics, exits, or ignores an event, the browser can wait indefinitely. Use a context deadline, log handler errors, and make the default branch continue requests. Keep the handler lightweight; perform slow work outside the event callback and preserve the request ID.

Verify that requests were actually blocked

Observe network events

Use chromedp network events or Chrome DevTools’ Network panel to inspect the request outcome. Reload a test page after installing the rules and look for the stylesheet and image requests. DevTools’ request-blocking workflow demonstrates the visible effect: blocking a stylesheet changes page styling.

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Use a controlled test page

1. Host a page that references a known external stylesheet and a known image URL.
2. Run the Network-blocking program with those exact patterns.
3. Record request events and confirm the URLs are marked blocked or failed.
4. Compare the page with and without the rules, checking both layout and network records.

Do not use the final screenshot alone as proof. A page can contain an inline image, a data URL, a cached element, or JavaScript fallback. A documented chromedp issue shows that a page may substitute a hard-coded image after an external image request fails, so an image remaining visible does not prove that its network request was allowed.

Common problems and fixes

CSS still loads

• Cause: the stylesheet URL has no .css suffix, is embedded in HTML, or was already loaded before rules were installed.
• Fix: install blocking before navigation, inspect the actual request URL, add a precise pattern, or use Fetch resource-type filtering.

Some image formats remain

• Cause: the site uses SVG, AVIF, data URLs, CSS background images, or extensionless endpoints.
• Fix: add the formats you intend to block, inspect request URLs, and use Fetch when classification is more reliable than suffix matching.

The page hangs with Fetch enabled

• Cause: a paused request was never continued or failed.
• Fix: handle every EventRequestPaused, continue non-target requests, and add a timeout so the job terminates instead of waiting forever.

The code does not compile

• Cause: generated cdproto APIs, enum constants, or method signatures differ from the example.
• Fix: inspect the package version selected by go list -m, read the generated Network and Fetch declarations, and adjust names to that version. Keep chromedp, cdproto, and Chrome versions aligned.

An image is visible despite blocking

• Cause: inline data, cache, a fallback, or an alternate request supplied the pixels.
• Fix: inspect all requests and page source; verify the specific URL you intended to block rather than judging the screenshot.

Performance, reliability, and operational notes

What blocking changes

Blocking requests reduces the resources the browser has to download and prevents CSS from affecting presentation. It does not guarantee a faster job: JavaScript, fonts, API calls, service workers, redirects, and server-side delays can still dominate navigation. No general bandwidth or speed percentage should be assumed; measure your own pages.

Cache and repeated runs

Run verification with a controlled cache state. A resource served from cache may not create the network activity you expect on a second run. Compare a clean context with a repeated navigation and record events in both cases.

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Security and correctness

Blocking CSS can make elements move or disappear, while blocking images can alter intrinsic dimensions and lazy-loading behavior. Scrapers that rely on selectors should wait for the structural element they need, not for visual styling. If a script requires an image response to resolve, failing that request may change application behavior.

Rule maintenance

Keep the block list close to the code that owns browser setup, document why each pattern exists, and test representative URLs after site changes. Prefer narrowly scoped patterns when a broad wildcard could block an API or script accidentally.

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curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webp

Python:

import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)

Node.js:

const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);

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FAQ

Can I block only images from one host?

Yes. Put that host in the URL pattern and combine it with the image suffixes you need, or use Fetch to decide per request. Test overlapping allow and block rules because pattern order matters.

Does blocking CSS stop inline styles?

No. Network blocking affects requests. Inline <style> elements and style attributes are already in the document and require a different page-manipulation approach.

Should I use Network blocking or Fetch in production?

Use Network blocking for stable, predictable URL lists. Use Fetch when resource type or request-by-request policy matters, and provide a handler for every paused request.

Frequently Asked Questions

Can I block fonts and JavaScript with the same approach?

Yes, if their URLs are predictable you can add matching Network URL patterns. For type-based decisions, extend the Fetch handler with the corresponding resource type, but test carefully because scripts and fonts can be required for page logic.

Will a blocked image still count as a failed page load?

It can change application behavior, but it is not evidence that the browser allowed the image. Inspect request events and the page’s fallback logic to determine what happened.

Quick Recap

Bestseller No. 1

Magicmoon 2-Pack 24 Inch Computer Privacy Screen Filter for 16:9 Monitor

Perfect For Open Workspaces: Great for maintaining screen privacy in open work spaces

$36.99

Bestseller No. 2

[2 Pack] 24 Inch Computer Privacy Screen Filter for 16:9 Widescreen Monitor

$59.99

Bestseller No. 3

SightPro 24 Inch 16:9 Computer Privacy Screen Filter for Monitor - Privacy Shield and Anti-Glare Protector

$39.99

Bestseller No. 4

Peslv 2-Pack 24 Inch 16:9 Computer Monitor Privacy Screen, WxH:532 * 299mm

$59.99

Bestseller No. 5

ZOEGAA [2-Pack Computer Privacy Screen Protector 24 Inch 16:9 Aspect Ratio

$36.99

Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.